Occurrences of Niobium and Tantalum Mineralization in Mongolia

Abstract

Niobium and tantalum are two rare metals that have similar physical and chemical properties and occur together in nature. They are considered to be strategic and critical materials for the economy and national security of many industrial countries. Both elements are on the 2022 List of Critical Minerals of the USA as well as on the European Union’s List of Critical Raw Materials. They rarely substitute for common elements in rock-forming minerals but are essential components in a range of rare minerals, particularly oxides and subordinately silicates. The economically important minerals are oxides. The columbite-tantalite and pyrochlore-microlite groups are the most common Ta- and Nb-bearing minerals. In Mongolia, primary niobium and tantalum mineralization includes two main types. The first type is mineralization associated with alkaline to peralkaline granites, pegmatites and syenites whereas the second type is related to the lithium-fluorine-rich peraluminous granites and related rocks (pegmatites and ongonites). The host rocks of both types of mineralization are the fractionated felsic rocks, which contain the primary magmatic ore assemblages associated with fractionation of magma rich in rare metals. Both assemblages were subsequently overprinted by the late magmatic to hydrothermal fluids, which remobilized and enriched the original mineralization. The newly formed ore mineral assemblages display complex replacement textures. In the case of peralkaline felsic rocks the processes produced the mineralization of Zr, Nb, heavy REE, Y, U, Th and Ta whereas peraluminous Li-F felsic rocks contain mainly mineralization of Sn, W, Ta, Li, and Nb. Mongolia hosts several promising occurrences of both types of Nb-Ta mineralization. However, they have not yet been sufficiently explored. Currently, the most promising is the occurrence in the Devonian Khalzan Buregtei peralkaline granites in northwestern Mongolia, where Nb-Ta is associated with REE and Zr mineralization. Mesozoic carbonatites of southern Mongolia do not host significant Nb and Ta mineralization.